DESCRIPTION: Vascularization is important for the treatment of various ischemic diseases and the survival of tissue-engineered constructs. Thus, the development of angiogenesis strategies has continuously attracted great attention in various fields. However, the realization o successful angiogenesis is challenging, because vascular formation and maturation involve multiple growth factors at different stages. Moreover, while insufficient angiogenic factors do not induce effective angiogenesis, excess angiogenic factors can lead to the formation of defective and leaky blood vessels. Thus, therapeutic angiogenesis requires not only multiple growth factors, but also mechanisms for modulating the time, dosage, and sequential order of growth factor delivery. While bolus injections are the simplest way to control the time, dosage, and sequential order of growth factor delivery, this mode of delivery requires very high levels of growth factors. It can lead to severe systemic toxicity. By contrast, polymeric delivery systems hold great promise for localized delivery of growth factors with reduced systemic toxicity. However, it is challenging to develop a polymeric system to control the release time, dosage and sequential order of multiple growth factors. The objective of this application is to develop a novel molecularly controlled release mechanism and a hydrogel-based polymeric system that can release multiple angiogenic factors with differential and independent timing and dose control, hence regulating angiogenesis in a dynamic manner. The central hypothesis is that multiple growth factors would be sequestered within the same hydrogel by specific binding to hydrogel-linked nucleic acid aptamers, and released specifically by competitive binding of complementary sequence (CS) triggers. To test this hypothesis, we will work on three specific aims: 1) to synthesize aptamer-functionalized superporous hydrogels (AS-gels) for high-capacity sequestration and retention of multiple growth factors; 2) to design and optimize aptamer and CS sequences and to determine molecularly regulated growth factor release from AS-gels in vitro; and 3) to investigate molecularly regulated growth factor release from AS-gels and angiogenesis in mice. We have performed preliminary studies and acquired compelling data showing that AS-gels can sequester growth factors and release them in the presence of CS triggers. More importantly, AS-gels can be triggered to release growth factors to stimulate angiogenesis in vivo. Therefore, the accomplishment of this project will lead to a novel strategy for on-demand delivery of multiple growth factors. It will benefit the treatment of various ischemic diseases such as repair of internal organs where it is too harmful or impossible to repeatedly inject growth factors directly into the tissue.